The invention concerns an alternating current power source for welding, in particular for TIG and electrode welding, for generating an alternating current from a three-phase current.
In the welding of metals, which form nonconducting and/or high-melting oxides, by the TIG process, it is necessary for the purpose of removing the oxide skin to operate either with reversed polarity (positive pole at the electrode), which is possible, however, only with low current intensities in view of the excessive generation of heat at the welding torch, or with an alternating current, which corresponds to the current practice.
In electrode welding with a direct current, blow effects are frequently encountered, which render the control of the arc impossible. Here, again, an alternating current must be used.
According to the prior art, welding transformers are used for this purpose, which are connected on the primary side to two phases of the three-phase supply network and wherein the welding current is regulated by means of scatter yoke cores, transductors or thyristors with phase-gating control.
Power sources of this type have the disadvantage of a high power requirement, which in the case of the welding currents usually required rapidly exceeds the available connected load. Another disadvantage is the asymmetrical loading of the three-phase supply network.
In order to eliminate these disadvantages, more recently power sources have been developed, which are connected to all three phases of the network and contain a three-phase bridge rectifier, together with a subsequent thyristor inverter or transistor inverter. As against conventional transformers with thyristors, such power sources are naturally complicated and expensive.